... reflection strength or impedance on each reflector.The algorithms are 'two and one-halfdimensional' (2.5-D) in that they incorporate three-dimensional (3-D) wave propagation in a medium which varies in only two dimensions. The use of 3-D sources does not entail any computational penalty, and it avoids...

...L. Eskola; Edson E. S. Sampaio Abstract In a recent paper Sampaio presented an analytic solution of the magnetic field problem for a circular magnetized cylinder embedded in a homogeneous magnetized half-space. In his paper, Sampaio also stated that the numerical method for solving magnetostatic...

...™ spectra are collected in three modules, one covering the visible to near-infrared wavelengths (VNIR: 380–1,000 nm) and two covering the shortwave-infrared (SWIR: 1,000–2,500 nm). The sampling interval of the ASD™ spectrometer is 1.4 nm in the VNIR and 2.0 nm in the SWIR, with a wavelength accuracy of ±1...

... survey conducted over five profiles on the lake in 1986, the purpose of which was to study the 1.1 Ga Midcontinent Rift under the lake. Two and one-halfdimensional (2.5D) magnetic modelling has demonstrated that the model predicted by the seismic results is compatible with the magnetic anomalies under...

...R. Gerhard Pratt; M. H. Worthington Abstract Previously published equations for diffraction tomography do not solve the 'two and one-halfdimensional problem' (point source illumination of two-dimensional geology) if sources and receivers are confined to linear arrays. In spite of this lack...

... which are 3-D points rather than lines. This configuration is denoted as two-and-one-half-dimensional. We present a frequency-domain approach to modeling acoustic wave propagation in such situations which allows correct treatment of point sources but takes advantage of the assumed 2-D nature...

... reconstruction algorithm similar to those used in seismic cross-well tomography or medical imaging applications.The technique was demonstrated using ray-theoretic examples to simulate radial variations in slowness. In addition, full-waveforms were generated using two-and-a-half-dimensional (2.5-D) FDM computer...

... deconvolution, and (6) two-and-a-halfdimensional (2.5-D) corrections. This preprocessing is designed to enhance scattered P-waves that are used in the inversions.Images obtained from the application of back-propagation and quadratic programming methods to the preprocessed data show possible fracture zones...

... compensated topography, and in which the area of interest is modeled using the seismic constraints applied in a two-and-one-half-dimensional geometry, holds promise for exploiting useful features of both the Bouguer and isostatic residual gravity anomalies. ...

A new isostatic residual gravity map of the conterminous United States presents continent-wide gravity data in a form that can be readily used, with geologic information and other geophysical data, in studies of the composition and structure of the continental crust. This map was produced from the gridded gravity data on which the recently released Gravity Anomaly Map of the United States is based. About 1 million onland and 0.8 million offshore gravity observations interpolated to a 4- by 4-km grid serve as the basis for both maps. The Airy-Heiskanen model of isostatic compensation of topography applied to topographic and bathymetric data averaged over 5- by 5-min compartments was used to remove, to first order, the large, long-wavelength Bouguer gravity anomalies caused by deep density distributions that support topographic loads. The parameters used in the Airy-Heiskanen model were topographic density, 2.67 g/cm 3 ; sea-level crustal thickness, 30 km; and density contrast across the base of the model crust, 0.35 g/cm 3 . Many of the conspicuous short-wavelength anomalies (widths less than several hundred kilometers) on the isostatic residual gravity map correlate with mapped or near-surface geologic features, and primarily reflect shallow-density distributions rather than any departures from isostatic equilibrium. In general, gravity highs occur over (1) mafic igneous bodies emplaced in rift or magmatic arc settings or as isolated intrusions controlled by structures; (2) accreted slices of mafic oceanic, island-arc, or transitional crust; and (3) uplifted crystalline basement. Gravity lows are found over (1) thick bodies of felsic intrusive or extrusive rocks; (2) sedimentary deposits in extensional, convergent, or transform settings; and (3) depressed crystalline basement. Anomalies with widths as much as 1,000 km or more also appear to reflect crustal properties in many cases—several broad gravity highs are associated with crust having a high average seismic wave velocity, and comparable broad gravity lows occur over areas of low average seismic velocity. Alternative ways of viewing the isostatic residual gravity data provide additional information about density distributions in the crust. The first-vertical derivative map accentuates gravity anomalies over shallow, abrupt density changes at the expense of those resulting from deeper or more gradual density transitions. The maximum horizontal gradient map contains information about the locations of pronounced density boundaries. Two-dimensional spectral analysis of the gravity data provides a quantitative means for identifying dominant fabrics in the gravity field and for distinguishing various terranes from each other. Neither Bouguer nor isostatic residual gravity anomalies are particularly well suited for practical modeling of deep structure in conjunction with deep seismic information. However, a scheme in which the entire Earth outside the area of interest is approximated by laterally homogeneous layers and isostatically compensated topography, and in which the area of interest is modeled using the seismic constraints applied in a two-and-one-half-dimensional geometry, holds promise for exploiting useful features of both the Bouguer and isostatic residual gravity anomalies.

... of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term 'two-and-a-halfdimensional' (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained...

... inversion schemes are of limited utility even in 2-D media because they do not model 3-D dynamics correctly. Many seismic experiments effectively assume that the geology varies in two dimensions only but generate 3-D (point source) wavefields; that is, they are 'two-and-one-half-dimensional' (2.5-D...

... gradiometry) which makes Bathurst a unique case. We show data compilation and map view interpretation, followed by two-and-a-half-dimensional (2.5D) gravity and magnetic modelling. From this, we provide constraints on the folded structure of the mafic and felsic volcanic units, and we interpret a large...

... Abstract Numerical implementation of multicomponent true-amplitude Kirchhoff imaging in two and one-halfdimensional v(x,z) media, requires the computation of several ray quantities: traveltimes, slowness, polarization vectors, and geometrical spreading. The purpose of this paper is to show...

Abstract Numerical implementation of multicomponent true-amplitude Kirchhoff imaging in two and one-half dimensional v(x,z) media, requires the computation of several ray quantities: traveltimes, slowness, polarization vectors, and geometrical spreading. The purpose of this paper is to show that all of these weighting (Green's) functions can be computed by means of the nonhyperbolic traveltime formula of (Tsvankin and Thomsen, 1994 ) and ( Hake et al., 1984 ) without any need of ray-tracing, in the case of vertically stratified VTI media. Such models are common in hydrocarbon exploration contexts, with a classical example being that of stratigraphic trap located within a horizontally layered sedimentary sequence. By means of nonhyperbolic traveltime function, we derive explicit approximations for the elastic Green's functions, applicable for multi-component true-amplitude Kirchhoff time and depth migration in vertically inhomogeneous VTI media. Numerical tests with synthetic data from 2D isotropic model show that the images computed by multicomponent true-amplitude Kirchhoff depth migration using explicit approximations of the Green's function compare well with results obtained based on dynamic ray-tracing. We have also succesfully applied the new elastic true-amplitude migration algorithm on 2D-4C OBC seismic data. The main advantage of the method is numerical efficiency rather than high accuracy. It may be of interest for prestack imaging of large data volumes and fast computation of prestack images of multicomponent data. Moreover, the proposed approach is well suited for migration velocity analysis for converted and non-converted waves in anisotropic media, where fast and repeated prestack migration is desired.

... for the area and process them using shaded relief, horizontal and vertical gradient, upward continuation, and layer stripping techniques to interpret the more subtle features of the fields.Traditional two and one-halfdimensional gravity and magnetic modelling is undertaken using constraints from...

... this contrast, a two and one-halfdimensional model shows that rocks of Tasiuyak domain constitute a triangular prismatic body with maximum thickness of 13 km adjacent to Nain Province, which thins westward to a feather edge. The model is compatible, qualitatively, with the aeromagnetic anomaly and consonant...

... of the azimuthal angle phi ), but the field generated by an off-axis source in this medium is in general a function of rho , phi , and z. This two and a half-dimensional (2.5-D) problem is often encountered in electromagnetic well logging, as well as in other areas such as optical fiber communications...